This invention relates to a system for establishing uniform distribution of fibers in a stock slurry prior to delivery of the stock to a forming surface of a papermaking machine.
It is highly important that paper stock when delivered to a paper forming surface be free of clumps, flocs, or agglomerations which can result in undesirable localized irregularities in the formed product, such as streaking and non-uniform density or thickness.
Numerous arrangements have been employed in the prior art in an attempt to obtain a generally uniform cross machine profile of deposited stock on the forming surface. Such prior attempts have included the use of complicated auxilliary equipment in the pre-slice area prior to deposition of the stock on the forming surface, such as rectifier rolls, holey rolls and other mechanical vibrating, shaking and stirring devices, all of which are characterized by their complexity of construction and high expense.
Another commonly used expedient employed to obtain uniform distribution of the stock material prior to entering a slice has been the use of multiple conduits or tubes for the stock positioned between the head box per se and the slice opening. Such arrangements attempt to obtain formation of a sheet of uniform thickness and density by breaking the stock proceeding from the head box down into separate stock flows and then recombining the flows. The theory behind such separate flow channels is that they facilitate stock mixing without impeding the smooth flow of the stock toward the slice opening. Such arrangements have the further advantage of employing only nonmovable or fixed elements, thus making them more reliable and less expensive than movable agitators or the like.
U.S. Pat. No. 2,688,276, issued Sept. 7, 1954 illustrates an example of a multi-tube arrangement employed to mix stock prior to its deposition on a forming surface. Several embodiments are illustrated in such patent including one wherein the tubes have deep serrations or V-cuts and sharpened edges at the downstream ends. Such a configuration is alleged in the patent to minimize disturbance of the forwardly flowing stock as it leaves the ducts or tubes.
Another multi-conduit configuration is illustrated in U.S. Pat. No. 3,725,197 wherein stock is flowed through a plurality of ducts, each of which progressively increases in diameter in the direction of stock flow in a series of steps. Successive different diameter portions of the ducts have a uniform cross section over the length thereof, and transition between two successive portions of the ducts has an opening angle of at least 100.degree., and preferably may be 180.degree..
Other representative patents illustrating usage of a plurality of stock flow tubes are U.S. Pat. Nos. 2,347,130, 3,238,236, 3,328,237, 3,400,044 and 3,846,229.